Tasmota uses a lot of String with constructs like below:

str->replace("aa", "bb);
str->replace(F("cc"), String(num));
str->startsWith(F("prefix"));
str->endsWith(F("suffix"));

Currently for any non String argument, the compiler silently instantiates a new Stringobject and deletes it after the call. This generates more than 1k of not very useful code.

This PR adds explicit methods to deal with common arguments const unsigned char * and const __FlashStringHelper *. It does not change the fact that a String object is created then deleted, it just reduces redundant code.

With this change, we see a 1k code size reduction with Tasmota.